api: Add go files

I know this is a huge commit, but I can't be bothered to check
this in part by part.

api/config_test.go

@@ -0,0 +1,33 @@
+package main
+
+import (
+	"os"
+	"testing"
+)
+
+func TestParseConfigBasics(t *testing.T) {
+	os.Setenv("ORIGIN", "https://commento.io")
+
+	if err := parseConfig(); err != nil {
+		t.Errorf("unexpected error when parsing config: %v", err)
+		return
+	}
+
+	// This test feels kinda stupid, but whatever.
+	if os.Getenv("PORT") != "8080" {
+		t.Errorf("expected PORT=8080, but PORT=%s instead", os.Getenv("PORT"))
+		return
+	}
+
+	os.Setenv("PORT", "1886")
+
+	if err := parseConfig(); err != nil {
+		t.Errorf("unexpected error when parsing config: %v", err)
+		return
+	}
+
+	if os.Getenv("PORT") != "1886" {
+		t.Errorf("expected PORT=1886, but PORT=%s instead", os.Getenv("PORT"))
+		return
+	}
+}